1. Field of the Invention
The subject invention is directed to gas turbine engines, and more particularly, to a system for actively controlling the combustion process in gas turbine engines to maintain combustion stability and optimize engine performance.
2. Background of the Related Art
Combustion instability is a significant problem in the design of low-emission, high performing combustion chambers for gas turbines. Combustion instability diminishes engine system performance, and the vibrations resulting from pressure oscillations can damage hardware components, including the combustion chamber itself. Combustion instability is generally understood as high amplitude pressure oscillations that occur as a result of the unstable coherent flow structures that develop from the turbulent nature of the combustion process and the large volumetric energy release within the combustion chamber. Moreover, when the combustion heat release becomes in phase with and reinforces acoustic pressure waves, a thermo-acoustic instability results.
In the past, passive control methods were employed to correct combustion instability, including, for example, modifying the fuel injection distribution pattern, or changing the shape or capacity of the combustion chamber. Passive controls are often costly and limit combustor performance. More recently, active control methods have been used to correct combustion instability by modifying the pressure within the system. This is done by sensing the amplitudes and frequencies of acoustic pressure waves, and then modulating fuel injection at the same frequencies but out of phase with the instabilities.
Currently, fuel injector flow rates are controlled by changing the fuel pressure feeding a common fuel manifold, with no individual control to each of the fuel injectors. Combustion stability could be achieved more effectively with active controls, if fuel flow could be modulated or pulsed at each fuel injector individually.
It would be beneficial therefore, to provide a combustion control system for gas turbine engines that is designed to command pulsed fuel flow to individual fuel injectors, so as to stabilize combustion and optimize engine performance.